Rubber rolls have found widespread use in a wide variety of applications. Processing rolls used in the textile industry, printing rolls used for press printing (i.e. ink transfer rolls), and fuser rolls in xerography copiers are all examples of the specific applications for rolls of the type herein described. Such rolls generally comprise an annular cylinder of elastomeric material such as silicone rubber, with a metal core typically being coaxially disposed within the roll for support. In all of these applications it is highly desirable to provide a jacket or sleeve around the outside surface of the rubber rolls in order to provide a low coefficient of friction so that resistance to the rotation of the roll in an adjacent surface is reduced. For this purpose, the sleeve is provided with a smooth outer surface and in addition, it is generally flexible so that the resilient character of the rubber will not be adversely affected during the operation of the roll. Fluorocarbon materials are quite suitable as a sleeve material, and are therefore often used. More specifically, polytetrafluoroethylene, which is commonly known as Teflon (registered trademark of Du Pont Corporation), and polytrifluorochloroethylene are examples of fluorocarbon sleeves which are frequently used.
Method and apparatus for manufacturing such sleeved rolls have been described in numerous patents assigned to the assignee of the present invention, including U.S. Pat. Nos. 3,380,120; 3,481,805; 3,607,494; 3,613,168; and 3,647,336. In particular, U.S. Pat. No. 3,613,168 describes a method of procuding a cored rubber roll while simultaneously placing a thin flexible sleeve thereon comprising: etching the inner surface of the sleeve, placing the sleeve into a mold casing and around a core member positioned in a casing, supporting the sleeve so as to provide a space between the core member and the sleeve, feeding rubber into the space between the core member and the sleeve, applying pressure to the rubber while feeding it into the space to thereby cause the rubber to accumulate and expand the sleeve against the inside of the mold casing, and continuing to feed the rubber into the spacing until all of the available space is filled between the core and the sleeve, thereby to fully expand the sleeve against the inside casing along substantially the entire length of the sleeve. In the preferred embodiment of the invention, the rubber is passed into the space from a number of directions so as to expand the sleeve substantially simultaneously in all directions. For this purpose the mold assembly is provided with end sections which include a plurality of small circular holes through which the rubber is passed in a plurality of streams. The holes are smaller than the space into which the rubber passes and as a result the pressurized rubber accumulates in the space near the holes and begins to expand the sleeve. After the sleeve in a particular area is expanded by the rubber against the inside mold casing, the continued passage of rubber into the same area causes the rubber to slowly travel along the axial length of the space between sleeve and core member with the consequent further periodic accumulation of the rubber and expansion of the sleeve. The process is continued until the rubber fills substantially all of the available space between the core and the sleeve. In this manner not only is the rubber formed about the core with precise dimensions but the sleeve is also simultaneously bonded to the rubber as it is pressed by the rubber under great pressure against the inside surface of the casing. After the rubber has filled the available space, the entire mold is removed and may then be placed in an oven and processed to a temperature at which the rubber is vulcanized. Thereafter, the assembly of core, rubber roll and sleeve is withdrawn from the mold and may be slowly heated to approximately 400.degree. F. for the purposes of driving off excess gases that may have been trapped within the rubber, if desired.
In certain applications these sleeved rolls are utilized in an environment containing chemicals which will cause deterioration of the rubber within the sleeved roll and thus adversely affect the longevity of the roll. For example, the fuser rolls used in xerography copiers are exposed to an oil (called fuser oil) which attacks silicone rubber and would greatly reduce the longevity of the fuser roll if means were not provided for protecting the silicone rubber thereof from the fuser oil. Fortunately, the cylindrical working surface of the rubber roll is easly protected from direct radial exposure to the fuser oil by selecting an appropriately oil-impervious fluorocarbon sleeve such as Teflon. The real problem has been to protect the rubber roll from fuser oil entering through the ends of the fuser roll and laterally attacking the silicone rubber.
The end of the fuser roll appears as a laminate of an inner metal core, an intermediate rubber body, and an outer fluorocarbon sleeve, the latter typically extending inwardly to some degree over the exposed end of the rubber body. The ends of the rubber body have heretofore been protected from the fuser oil to some degree by the application thereto of an oil-impervious sealer, such as a special room temperature vulcanizable elastomeric material of fluorosilicon rubber hereinafter referred to as "RTV" and available from Dow Corning under the designation of "DC 236 Dispersion". The sealant is applied to the rubber body end in such a manner as to cover the entire exposed end surface of the rubber body, and overlap the adjacent end portions of the fluorocarbon sleeve and metal core, thereby hopefully to seal the end of the rubber body between the sleeve, core and sealant. Unfortunately while the RTV sealant bonds in a fairly satisfactory manner to the rubber body and to the metal core and thus precludes the intrusion of fuser oil through the end of the rubber body and between the outer surface of the metal core and the inner surface of the rubber body, it does not bond as well to the Teflon sleeve. The latter eventually breaks away from the sealant after a period of use and permits intrusion of fuser oil between the inner surface of the sleeve and the outer surface of the rubber body.
To combat migration of the fuser oil between the sleeve and rubber body, the fuser rolls are often provided with ends having beveled outer edges wherein the inner surface of the sleeve is tightly pressed against the outer surface of the rubber edge to block the migration path. For example, in the process disclosed in U.S. Pat. No. 3,481,805, wherein heat shrinkable plastic sleeve is heat-shrunk about a rubber roll to bond the sleeve thereto, the heating is prolonged at each end of the roll to cause additional shrinkage of the sleeve ends so that a bevel is formed at the outer edge of the roll end. Similarly, in the process disclosed in U.S. Pat. No. 3,613,168, wherein rubber is injected between a metal core and an expandable plastic sleeve to radially expand the sleeve and bond the rubber to both core and sleeve, each end of the sleeve is maintained at its original diameter as the intermediate length of the sleeve is radially expanded so that a bevel is formed at the outer edge of the roll end. Nonetheless, experience has shown that once even a slight gap arises at the sleeve/sealant interface at the roll end, the fuser oil will intrude through this gap and in time work its way through the sleeve/roll interface at the bevel.
As improvements in the materials and manufacturing techniques for making these sleeved rolls have improved, the problem of effectively sealing the sleeved roll ends has become more important; in fact the critical factor determining the longevity of the currently available fuser rolls is presently the effective life of the end seal. To fully appreciate the magnitude of the problem, it must be recognized that when the sleeve is composed of a "release" material such as Teflon, only the inner surface of the sleeve end is truly available for bonding, as it is only the inner surface of the sleeve which has been etched to permit bonding. Furthermore, it must be recognized that it is characteristic of an injection molded sleeved roll (for example, one manufactured by the process described in U.S. Pat. No. 3,613,168) that the ends of the roll are of slightly greater diameter than the intermediate length of the roll. As a result, these roll ends are subjected to great flexing during use, and hence the likelihood of sleeve/sealant separation at the roll ends is extremely high.
Accordingly, it is an object of the present invention to provide a sleeved roll with an improved end seal.
It is another object to provide such a sleeved roll wherein the ends of the rubber body are protected against attack by harmful fluid by use of a sealant.
It is a further object to provide such a sleeve roll wherein the rubber body is protected from attack even after harmful fluid has migrated between the sealant and the sleeve.